I tried to recreate the issue.I had added 10 images for example and unmarked the autogenerate titles checkbox.After that i opened the interface and the checkbox was there waiting for another image to be added. I didn't added any image and clicked o.k. with the checkbox filled. No Alt tags were generated because the extension had remembered my previous settings for the images. After that i added one image with the checkbox filled and the alt tag was applied only to that image.
Sorry to say but that doesn't help me fix the issue here.
I understand that the program works, most of the time, but there is a problem here this time. I need to find out what it is or else go to all the extra work of manually deleting the auto generated titles.
I explained before what I did to cause the problem but if I need to give more of an explanation please let me know.
The extension is constructed to work that way currently. The only way to avoid the not desired alt tags is to recreate the slider and make sure that Auto Generate Image tittles is unchecked everytime you want to add new folder with images or new image slide.